Atomic force microscopes and scanning electron microscopes are previously known as apparatuses that can measure spatial features of a microscopic three-dimensional object, such as a cell, with nanometer accuracy. However, with the use of an atomic force microscope or a scanning electron microscope, it is often necessary prior to measurement to subject a cell to a troublesome pretreatment, and the cell will suffer irreparable damage during measurement. Therefore, studies have been conducted on a variety of apparatuses that can measure spatial features of a microscopic three-dimensional object, such as a cell, without damaging the sample.
For example, Patent Literature 1 proposes a quantitative phase microscope that can measure a sample, such as a cell, without damaging it.
FIG. 8 shows a schematic block diagram of a quantitative phase microscope 100 described in Patent Literature 1. As shown in FIG. 8, the quantitative phase microscope 100 includes an objective lens 102, a total reflection mirror 103, a transmissive polarization splitting element 104, a condensing lens 105, a spatial filter 106, a half-wave plate 107, and a complex lens 108, which are arranged in this order between a measurement sample S and an image pickup device 101.
In the quantitative phase microscope 100, light H101 to be measured having passed through the measurement sample S is converted into parallel light H102 by the objective lens 102. The light H102 is reflected toward the transmissive polarization splitting element 104 by the total reflection mirror 103.
The light H102 is split, in the transmissive polarization splitting element 104, into a beam H103a traveling straight ahead and through the element 104 and a beam H103b refracted to the beam H103a. These beams H103a and H103b are linearly polarized beams whose polarization directions are orthogonal to each other.
Next, the linearly polarized beams H103a and H103b are converted into converging beams H104 (H104a and H104b), respectively, by the condensing lens 105 and focused on an aperture 106a and a pinhole 106b, respectively, of the spatial filter 106.
The converging beam H104a passing through the aperture 106a is emitted as an object beam H105 holding the same phase information as the light H101 to be measured.
On the other hand, the converging beam H104b passing through the pinhole 106b is converted into a reference beam H106 devoid of the same phase information as the light H101 to be measured and having only information of a uniform phase different from the phase of the light H101 to be measured. The reference beam H106 is polarized to have the same polarization direction as the object beam H105 by the half-wave plate 107 disposed behind the spatial filter 106.
The object beam H105 and the reference beam H106 are superposed at the complex lens 108 to form interference fringes. The image pickup device 101 takes an image of these interference fringes. The phase information of the light to be measured is quantified from the taken image of interference fringes.